What is the OSI Model?
OSI is an acronym for Open Systems Interconnection. The International Organization for Standardization (ISO) created the OSI model (ISO). It’s a model for how applications communicate over the internet. In order to facilitate interoperability between diverse devices and applications, the OSI model describes computing functions into a universal set of rules and standards.
The OSI model can be thought of as a universal computer networking language. It is built on the divide-and-conquer concept, and it divides the communication system into seven abstract layers, each of which is layered on top of the previous layer.
The OSI is made up of seven levels, each of which performs a different network function. The OSI model breaks down the process into seven smaller, more achievable steps.
Each layer is given a certain task. Each layer is self-contained, allowing each layer’s tasks to be completed individually.
The OSI model is divided into seven layers. –
- Physical Layer
- Data Link Layer
- Network Layer
- Transport Layer
- Session Layer
- Presentation Layer
- Application Layer
What is the TCP/ IP Model?
TCP/IP is an acronym for Transmission Control Protocol/ Internet Protocol. The OSI Model we just looked at is merely a logical/reference model. It was created to define the communication system’s functions by breaking down the communication process into smaller, more manageable components.
However, the TCP/IP concept, which is based on standard protocols, was designed and developed by the Department of Defense (DoD) in the 1960s. TCP/IP is a simplified version of the OSI model. It has four layers, as opposed to the OSI model’s seven. The layers are as follows:
- Application Layer
- Transport Layer
- Internet Layer
- Network Access Layer
Why do we still use the OSI Model?
When it comes to security, practitioners must keep a number of things in mind. Within a networking stack, the OSI (Open Systems Interconnection) architecture provides the principles needed to manage both technical concerns and risks.
Despite the fact that information security is changing to a cloud-first environment, the OSI model remains relevant. The following are the reasons why the OSI Model remains to be relevant:-
- Helps in identifying threats throughout our tech stack –
For decades, the OSI model has been used to help IT professionals understand networking and resolve problems that might occur at any point during the networking process.
As a result, it’s still useful for infosec professionals conducting asset inventories today. Using the different layers, you may classify your physical assets, any data you might have on your organization’s networks (and how it’s protected), and an inventory of which applications your employees use to access your data and resources. The approach can also assist you in addressing vulnerabilities and security issues according to the layers they impact.
- Makes it possible to have a data-focused security posture –
The OSI model is effective in helping you determine where the biggest data security threats are inside your business, since it provides a framework for doing an inventory of your firm’s assets. Knowing where the majority of your company’s data is held, whether on-premises or in cloud services, will help define your information security policy. You can invest in the correct solutions that provide you data visibility within the proper OSI layers once you have this knowledge.
For example, if you know that a lot of your sensitive data is stored in SaaS services, you’ll need an API-driven data discovery solution, rather than an endpoint manager, to monitor and safeguard that data.
Given that many data compliance regimes demand you to demonstrate that your controls are suitably customized to the environments where your data resides, having this data-centric view is critical not only for security but also for compliance.
- Enables cloud adoption via a security first approach –
Given how important the OSI model is for completing an inventory of your security resources and assets, it is no surprise that using it when migrating to the cloud might be beneficial. This is because the OSI model will assist you in identifying the precise types of data security concerns that cloud adoption may pose to your company.
- Secures cloud infrastructure as well –
Several experts have developed “updated” OSI models that reflect operational layers in IaaS (Infrastructure as a Service) and cloud architecture. While the OSI system layers can be applied in a variety of ways to cloud architecture, it’s evident that the model is conceptually flexible.
With this in mind, it may be worthwhile to examine your own cloud architecture and determine whether designing a modified OSI model for your surroundings might enhance your security program.
The Open System Interconnection (OSI) paradigm has established a uniform vocabulary for networking conversations and documentation. This allows you to dissect and evaluate the components of a complex communication process. While this paradigm is not directly implemented in today’s TCP/IP networks, it is a useful conceptual model for relating multiple technologies to one another and implementing the appropriate technology in the appropriate way.
It provides a shared basis for the coordination of standards development for the goal of systems interconnection while allowing current standards to be placed into context within the overall reference model. The approach can be used to design new standards as well as to think about existing ones. We can think about our network in chunks or layers using the OSI paradigm. You may concentrate on securing, optimizing, and troubleshooting each layer separately.
Understanding the Layers of the OSI Model :
1. Physical Layer –
The physical layer is the lowest layer in the OSI reference model. It is in charge of establishing a physical connection between the devices. Bits of information are stored in the physical layer. It is in charge of sending individual bits from one node to another. When this layer receives data, it converts the signal received into 0s and 1s and sends them to the Data Link layer, which reassembles the frame.
The following are the functions of the physical layer –
- Bit synchronization –
A clock is provided by the physical layer, which allows the bits to be synchronized. This clock controls both the sender and the receiver, ensuring bit-level synchronization.
- The transmission rate, or the number of bits transferred per second, is likewise defined by the Physical layer.
- The physical layer defines the arrangement of devices/nodes in a network, such as a bus, star, or mesh topologies.
- The physical layer also specifies how data is passed between the two linked devices. Simplex, half-duplex, and full-duplex transmission modes are available.
2. Data Link Layer –
The data link layer is in charge of message transport from node to node. The major purpose of this layer is to ensure that data transfers from one node to another through the physical layer are error-free. It is DLL’s responsibility to transmit a packet to the Host using its MAC address when it comes to a network.
The following are the functions of the data link layer –
- The data link layer is responsible for framing. It allows a sender to deliver a set of bits to a receiver that is relevant to the receiver. This can be done by attaching unique bit patterns to the frame’s beginning and end.
- After producing frames, the Data Link Layer adds the sender and/or receiver’s physical addresses (MAC addresses) to the header of each frame.
- The data link layer implements error control by detecting and retransmitting broken or lost frames.
- Because the data rate on both sides must be constant or the data may be corrupted, flow control coordinates the amount of data that can be transferred before the acknowledgement.
- When many devices share a single communication channel, the MAC sub-layer of the data link layer assists in determining which device has control over the channel at any particular time.
3. Network Layer –
The network layer is responsible for data transmission between hosts on different networks. It also handles packet routing, which is the choosing of the shortest route to send a packet from a large number of options. The network layer places the IP addresses of the sender and receiver in the header.
The following are the functions of the network layer –
- The network layer protocols determine which route from source to destination is most appropriate.
- The network layer defines an addressing scheme in order to uniquely identify each device on the network. The IP addresses of the sender and receiver are inserted in the header by the network layer. An address like this recognizes each gadget in a unique and universal way.
4. Transport Layer –
The application layer receives services from the transport layer, while the network layer receives services from the transport layer. Segments are the units of data in the transport layer. It is in charge of the full message’s delivery from beginning to end. If an error is detected, the transport layer acknowledges the successful data transmission and re-transmits the data.
The following are the functions of the transport layer –
- This layer takes the message from the (session) layer and divides it into smaller chunks. A header is connected with each segment that is created. The message is reassembled by the transport layer at the destination station.
- The transport layer header provides a form of address called service point address or port address in order to deliver the message to the relevant process. The transport layer ensures that the message is delivered to the relevant process by supplying this address.
5. Session Layer –
This layer is in charge of establishing connections, maintaining sessions, authenticating users, and ensuring security.
The following are the functions of the session layer –
- Synchronization –
This layer allows a process to insert checkpoints into the data that serve as synchronization points. These synchronization points to aid in the detection of errors so that data may be correctly resynchronized, message ends are not served prematurely, and data loss is avoided.
- The session layer enables two systems to begin communicating in half-duplex or full-duplex mode. The layer facilitates the establishment, use, and termination of a connection between the two processes.
6. Presentation Layer –
The Presentation layer is also known as the Translation layer. The data from the application layer is retrieved and processed here so that it may be transmitted across the network in the proper format.
The presentation layer’s functions are as follows –
- It implements translation. For example, ASCII to EBCDIC translation.
- It implements data encryption. Data encryption converts information into a different format or code. The ciphertext is the encrypted data, while the plain text is the decoded data. When encrypting and decrypting data, a key-value is used.
- It decreases the amount of data that must be sent over the network.
7. Application Layer –
The Application layer, which is implemented by network applications, is at the very top of the OSI Reference Model stack of layers. Applications generate the data that must be sent across the network.
This layer also acts as a window for application services to connect to the network and show the information they receive to the user. The application layer’s functions are as follows –
- It allows a user to connect to a distant host via a network virtual terminal. At the remote host, the application produces a software emulation of a terminal. The computer of the user communicates with the software terminal, which communicates with the host, and vice versa. The remote host then thinks it’s talking to one of its own terminals and lets the user log in.
- Mail and Directory Services.
- File Transfer Access and Management.
Abstraction is possible with the OSI layered model (as explained). The higher layers are not required to understand how the lower layers perform their duties.
Furthermore, the lower layers are not required to understand what the upper layers are doing with the fruits of the lower layers’ labor. Because of this abstraction, you can communicate on the Internet using the same web browser and HTTP protocol, regardless of whether the lower-layer connection is a dial-up modem, a high-speed Internet connection, or something in between.
The speed or performance that results will undoubtedly differ, but the functionality will not. Thus, OSI is still relevant in today’s world as it provides for the basic concepts in networking.
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